Naomi Cavaday
BBC Radio 5 Live Sports Extra tennis commentator

This is once again a really physical test for Williams, as it was in the last round against Sloane Stephens.

I think she'll start ramping it up on the second serve and start crunching her returns that bit more.

Second break-point chance and this time Williams, thanks to a great cross-court shot takes it. Back on serve.

Sakkari gets lucky as the ball flicks off the net and just about lands in. That was on break point down so a good time to get fortunate.

A break-back point for Williams.

British pairing Jamie Murray and Neal Skupski have lost their men's doubles quarter-final against Croatia's Mate Pavic and Bruno Soares of Brazil.

Williams, 38, is trying to muster all the energy she has got and the screams are getting louder at every shot. But a hold to 15, Sakkari with a break in the decider though.

A mixed service game for Sakkari with an ace and a double fault but Williams then pulls a forehand wide, which after a quick check, means Sakkari has a 2-0 lead.

Naomi Cavaday
BBC Radio 5 Live Sports Extra tennis commentator

If Williams can raise her level one degree we know that would be enough but can she do it?

Russell Fuller
BBC tennis correspondent

Williams looked disgusted with herself at losing her serve. She looked comfortably the better player in the first set and we thought we were looking at a straight sets win.

Williams goes long. That's a break for Sakkari, her first of the day, and this match has completely turned around. Williams won the first set, Sakkari now a break up in the decider.

A stunning cross-court winner from Sakkari as Williams advanced gives the 15th seed a break point chance at the start of the third set.

Deuce in game one of the final set on the Williams serve.

When these two met at this stage of the Western and Southern Open a couple of weeks ago, Williams won the first set and then Sakkari took the second on the tie-break.

That's the scenario we've got again now. Two weeks ago, Sakkari breezed through the deciding set 6-1. Will history repeat itself?

Naomi Cavaday
BBC Radio 5 Live Sports Extra tennis commentator

Sakkari will be full of confidence now. She's been standing further up the court and starting to do some damage to Williams.

Sakkari can't take her first four set points, but she can take the fifth and that means it is one set all. Sakkari wins the tie-break 8-6.

We've got a lot more life left in this one.

Into a decider.

Three set points saved, make that four as Williams with another brute force shot leaves Sakkari stranded. 6-6.

This is Sakkari's third set point, but Williams, from the baseline, sends a blistering forehand and then a stunning backhand to mix it up. 6-5 Sakkari.

But Williams, off her own serve, loses the 10th point to give Sakkari two more set points. 6-4, Sakkari.

Williams turns up the power and that wins her another point. She trailed 4-0, now it's 5-4 to the Greek.

Naomi Cavaday
BBC Radio 5 Live Sports Extra tennis commentator

It feels like the balance of the Williams game is bouncing around whereas Sakkari's game seems a little bit more solid.

I've just settled into a comfort zone that we might have a long time to go in this match but we might only be a few points away from a Williams victory.